It is established practice to provide connectors for plain end pipes which utilise friction rings or hardened grippers to which force is applied by means of associated nuts and bolts. However, with such arrangements, the force applied by the nuts and bolts is often only partially transmitted to the friction ring or gripper, with the result that the pressure rating of the connection is relatively low--typically between 10 and 20 bars--because of the tendency of the pipes to move longitudinally relative to one another.
It has been proposed to alleviate this problem of movement of the pipes by providing fixed anchors for the pipes at regular intervals therealong, but this is a complex, time-consuming and expensive exercise.
More recently, somewhat more efficient connectors have been introduced which utilise a non-compressible fluid such as grease to urge a gripper in the form of a serrated ring of hardened steel into contact with the pipe, such connectors further including additional sealing means for sealing between the connectors and the outer surfaces of the pipes.
For example U.S. Pat. No. 3,582,112 discloses a pipe coupling including gripping means in the form of a pair of semi-circular grippers urged by a separate sealing ring of complex configuration into gripping engagement with the pipe.
However these known arrangements suffer from various disadvantages, not the least of which is that the grippers, being ring-shaped, cannot provide effective gripping around the whole circumference of other than precisely circular pipes, while the sealing means, being separate from the grippers, require independent actuation.